Headquarters Daily report APRIL 06, 1994 *************************************************************************** REPORT NEGATIVE NO INPUT ATTACHED INPUT RECEIVED RECEIVED HEADQUARTERS X REGION I X REGION II X REGION III X REGION IV X *************************************************************************** PRIORITY ATTENTION REQUIRED MORNING REPORT - HEADQUARTERS APRIL 6, 1994 MR Number: H-94-0033 NRR DAILY REPORT ITEM GENERIC COMMUNICATIONS BRANCH/EVENTS ASSESSMENT BRANCH DIVISION OF OPERATING REACTOR SUPPORT OFFICE OF NUCLEAR REACTOR REGULATION Subject: N/A NRC Information Notice 92-51, Supp. 1, "Misapplication and Inadequate Testing of Molded-Case Circuit Breakers," to be issued April 11, 1994. NRC is issuing this information notice supplement to clarify the original information notice and to provide additional references and information. On July 9, 1992, the NRC issued information notice 92-51, "Misapplication and Inadequate Testing of Molded-Case Circuit Breakers," (MCCBs). This notice was intended to inform addressees about some of the problems that NRC inspectors had discovered in the field that can cause and had been causing certain MCCBs to trip when starting their safety-related motor loads. Technical contact: Stephen Alexander, NRR (301) 504-2995 PRIORITY ATTENTION REQUIRED MORNING REPORT - REGION II APRIL 6, 1994 Licensee/Facility: Notification: Florida Power & Light Co. MR Number: 2-94-0025 Saint Lucie 1 Date: 04/06/94 Ft. Pierce,Florida Dockets: 50-335 PWR/CE Subject: FOLLOW UP TO REACTOR TRIP DUE TO CONTROL ELEMENT ASSEMBLY MOTOR GENERATOR CIRCULATING CURRENTS Reportable Event Number: 27035 Discussion: Unit 1 experienced a reactor trip from 19 percent power due to an overcurrent condition experienced by the two Control Element Assembly (CEA) Motor Generator (MG) sets which were operating in parallel. The event chronology is discussed below. On April 2, 1994, St. Lucie Unit 1 was undergoing a turbine startup. Per procedure, operators attempted to shift the "A" train electrical supply from its [offsite power feed] startup transformer to its [main generator output feed] auxiliary transformer. The startup transformer output circuit breaker (Westinghouse Model No. 50DHP) serving the 1A2 4.16 KV bus failed to automatically open as designed when the comparable auxiliary transformer output breaker closed. The startup transformer feed was immediately isolated from the Control Room by a redundant series breaker. The "A" startup transformer and 1A2 bus are in the "A" train "offsite power to onsite class 1E distribution system" path discussed in TS 3.8.1.1, and are the normal supply to the 1A3 "emergency diesel generator (EDG) output" bus. The 1A3 bus, in turn, powers the 480V "A" CEA MG set via a transformer. The "B" CEA MG set is similarly powered from the "B" train. The "A" and "B" CEA MG set outputs are paralleled for reliability and feed the unit's CEAs through trip circuit breakers (TCBs). The licensee concluded that personnel safety mandated that they deenergize the 1A2 bus prior to racking out the failed breaker. The licensee prepared a procedure for the activity, which included starting the 1A EDG to power the 1A3 bus and thus the "A" side 4.16 kV and 480 V loads normally supplied by the 1A3 bus. This included the "A" CEA MG set. The 1A EDG was started and loaded. When the 1A2/1A3 tie breaker was opened, the 1A EDG assumed an isochronous (constant frequency) mode of operation, as designed. This EDG control mode change resulted in a frequency difference between busses powered by the 1A EDG and those in train "B," powered from offsite sources. For most loads, the frequency change made no difference, however it did affect the CEA MG sets. The frequency difference caused the "A" CEA MG set to attempt to speed up, leading to a mismatch in the output phase angle of the two paralleled CEA MG sets. Within about 3/4 of a second, circulating currents and low output voltage resulted - producing overcurrent trips of several TCBs and one CEA MG set output breaker. The resulting CEA bus low voltage, either caused by low output voltage or open TCBs, was sensed by relays that caused a turbine trip as designed. The turbine trip, in turn, resulted in a reactor trip via the normal reactor protection system. Following a normal post-trip response, the 1A2 bus was isolated, the subject breaker was replaced, and Unit 1 was restarted. The failed breaker was sequestered pending arrival of a vendor representative. Regional Action: The resident inspectors are following both the licensee's investigation into the cause of the breaker failure and lessons learned from the CEA bus response and reactor trip. Contact: STEVE ELROD (407)464-7822 PRIORITY ATTENTION REQUIRED MORNING REPORT - REGION IV APRIL 6, 1994 Licensee/Facility: Notification: Gulf States Utilities Co. MR Number: 4-94-0025 River Bend 1 Date: 04/06/94 St Francisville,Louisiana RI Telecon Dockets: 50-458 BWR/GE-6 Subject: ESF ACTUATION Reportable Event Number: 27047 Discussion: Update on the loss of 230 KV line and subsequent ESF actuation. At 1:54 a.m. on April 6, 1994, the plant experienced a half MSIV isolation, start of both gas treatment systems, and several other equipment actuations as a result of an electrical grid perturbation when severe weather caused a ground on a 230 KV line. A static line over the 230 KV line broke, near Baton Rouge, Lousiana, and draped over the 230 KV line. When the dispatcher attempted to reenergize the 230 KV line, the system experienced voltage fluctuations which were felt as far away as Arkansas Nuclear One. Operators responded to the event by walking down their control panels and restoring equipment to normal conditions. The licensee has formed an investigation team to assess the response of the plant and to determine the cause of the individual equipment actuations. Regional Action: The resident inspectors are monitoring the licensee's efforts. Contact: J. I. Tapia (817)860-8243